Induction of Thiamine Inadequacy and Polioencephalomalacia in Adult Sheep with Amprolium

Abstract

SUMMARY Each day for 18 to 44 consecutive days, 7 adult sheep were intraruminally given large doses (880 mg./kg. of body weight) of amprolium, a structural analogue of thiamine. Before and at 1-week intervals after amprolium administration was begun, clinical examinations were made, and measurements were made of feed consumption; body weight; cardiac output; serum sodium, potassium, and magnesium concentrations; venous pH, carbon dioxide tension (P CO 2 ), and packed cell volume; blood pyruvate and total lactate concentrations; erythrocyte transketolase activity and thiamine pyrophosphate ( tpp ) effect; blood total thiamine concentration; and blood and ruminal content amprolium concentrations. Necropsies were performed. After approximately 6 weeks, 3 of the sheep developed clinical signs, and on necropsy, lesions were seen which were characteristic of polioencephalomalacia ( pem ), also known as cerebrocortical necrosis ( ccn ), a disease of cattle and sheep which is associated in the field with thiamine diphosphate ( tdp ) inadequacy. These 3 sheep also had biochemical evidence of tdp inadequacy. Four sheep survived for approximately 3 weeks and did not develop pem ; because biochemical indications of tdp inadequacy were not pronounced, it was concluded that the 4 sheep succumbed to amprolium toxicosis not associated with tdp inadequacy. Although myocardial and Purkinje's network lesions were seen, cardiac output remained essentially unchanged in amprolium-treated sheep with both types of responses.